3 Answers
3

Preheating is mainly needed for breads and anything that has a short cooking time (< 15 mins or so). I don't bother preheating when I'm roasting something for a longer time. If you're setting a timer, I assume this is something that will take a while to cook, so I wouldn't worry about preheating.

Don't do this with your pizza but braising, roasting and casseroles seem to do OK without preheating. I'm OK with beef sitting in the oven without refrigeration but I have to brine chicken and pork to preserve it a little and it seems to help with taste and juiciness anyway.

I seldom preheat for the kind of cooking I do. Things like cookies and cakes probably need to be preheated. Anything where you cooking for long periods of time, especially if the food starts out cold, should be fine. The only thing to be careful of is how long the food will sit in the oven before it comes on.